The invention relates to compressors. More particularly, the invention relates to sound and vibration suppression in screw-type compressors.
In positive displacement compressors, discrete volumes of gas are: trapped at a suction pressure; compressed; and discharged at a discharge pressure. The trapping and discharge each may produce pressure pulsations and related noise generation. Accordingly, a well developed field exists in compressor sound suppression.
One class of absorptive mufflers involves passing the refrigerant flow discharged from the compressor working elements through an annular space between inner and outer annular layers of sound-absorptive material (e.g., fiber batting). US Patent Application Pub. No. 2004/0065504 A1 discloses a basic such muffler and then improved versions having integral Helmholtz resonators formed within the inner layer. The disclosure of this '504 publication is incorporated by reference herein as if set forth at length.
International Applications PCT/US04/34946 and PCT/US05/03403 disclose further muffler configurations. Exemplary embodiments of these mufflers use inner and outer stacked rings of sound absorbing material. Exemplary ring material is expanded polypropylene beads (e.g., material known as porous expanded polypropylene (PEPP)). The disclosures of these applications are incorporated by reference herein as if set forth at length.